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Earth and Space Science
Lecture 1: The Ocean Floor
(Chapter 13)
The Oceans
• 71% of Earth is covered by Water
– 61% of the Northern Hemisphere
– 81% of the Southern Hemisphere
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Plate Tectonics
Mapping the Ocean Floor
Bathymetry: The
measurement of ocean
depths and the charting
of the topography of the
ocean floor.
Mantle Convection
Ocean
Floor
Magnetic
Stripes
• New oceanic crust records Earth’s
magnetic field when it forms
• Spreading seafloor moves away from
the ridge as newer crust is formed in a
conveyor belt fashion
Age of the Ocean Floor
Cross Section of the Ocean Floor
Continental Margins
• Are the outer margins of the continents
where continental crust transitions to
oceanic crust.
Types of Continental Margins
Turbidity Currents
Are downslope movements of dense, sediment-laden water.
Features of the Deep Ocean
Deep-ocean
Trench
• Are long, relatively
narrow troughs that are
the deepest parts of the
ocean.
• Most trenches are
located along the
margins of the Pacific
Ocean, where many
exceed 10 km (6 miles)
in depth.
Abyssal plain
• Are deep incredibly
flat features; in
fact, these regions
are likely the most
level places on the
Earth.
Volcanic Structures on the
Ocean Floor
Coral Atolls
Coral Atolls are ringshaped structures
that often extend
from slightly above
sea level to depths of
several thousand
meters
Seamounts and Volcanic
Islands
• Seamounts are
submarine volcanoes
that can rise hundreds of
meters above the
surrounding topography.
• Some grow large
enough to become
oceanic islands, but
most do not have a
sufficiently long eruptive
history to build a
structure above sea
level.
Guyots
•
•
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During their existence, inactive volcanic islands are gradually but inevitably
lowered to near sea level by the forces of weathering and erosion.
Submerged, flat-topped seamounts that formed in this manner are called
guyots.
Mid-ocean Ridge
Is a broad linear swell called a rise that is formed
along well-developed divergent plate boundaries.
The Wilson Cycle
• The cycle of
opening and closing
of Ocean Basins
• In plate tectonic
theory, plates rift
into pieces,
diverging apart and
new ocean basins
are born.
• Followed by motion
reversal, and plates
converging back
together, with plate
collision and
mountain building.
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Act 1 Scene 1: Birth
Continental Rifting Eg.
East African Rift Zone
Act 1 Scene 2:
Youth
Narrow Ocean Basin
Eg. The Red Sea
Act 1 Scene 3:
Adolescence
Maturing Ocean
Basin
Eg. Atlantic Ocean
Act 2 Scene 1:
Maturity
Subduction at Basin
Margins
Eg. Pacific Ocean
Act 2 Scene
2: Old Age
Subduction
Dominates, Basin
Narrows
Eg. Mediterranean
Sea
Act 2 Scene
3: Death
Continental Collision, Closing of the
Ocean Basin
Eg. Tethys Sea